The present invention is related to a fastener assembly for securing two or more members together, and more particularly to a fastener assembly that is plastically deformable at a preselected load to provide a maximum load limit therefor without attendant failure. A plurality of such fastener assemblies may be used to provide a progressively loadable mounting joint for more positively securing a workpiece to a frame.
Conventional rollover protection structures for vehicles include sturdy beams which extend over the head of the operator and two or more depending legs which are usually removably secured to the frame by a plurality of fasteners. In the typical case the frame has threaded apertures formed therein, and a plurality of bolts extend through flanges on the legs and are screw threadably received in the apertures. When the rollover protection structure is subjected to relatively instantaneous loads of high magnitude, as would be the case in the event of an accidental rollover of the vehicle, the individual bolts holding the legs to the frame are subject to progressive failure. Since the bolts are often aligned in rows, the mounting joint tends to open at one location subjecting the leading one of the bolts to a greater stress than the others. As a result, such heavily stressed bolt may reach its tensile yield load and fail by breakage before the remaining bolts can pick up and share the remaining load. This can cause the other bolts to fail in a sequentially following manner. Heretofore, in an attempt to solve this problem such mounting joints have used an excessive number of bolts or larger bolts than necessary, or have been completely redesigned to a more costly form of construction.